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Date: Sun, 18 Aug 2013 17:22:42 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] powerpc iommu: enable multiple TCE requests
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To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, Paul Mackerras <paulus@samba.org>, David Gibson <david@gibson.dropbear.id.au>

Il 16/08/2013 11:49, Alexey Kardashevskiy ha scritto:
> With KVM, we could fall back to the qemu implementation
>> +     * when KVM doesn't support them, but that would be much slower
>> +     * than just using the KVM implementations of the single TCE
>> +     * hypercalls. */
>> +    if (kvmppc_spapr_use_multitce()) {
>> +        _FDT((fdt_property(fdt, "ibm,hypertas-functions", hypertas_propm,
>> +                           sizeof(hypertas_propm))));
>> +    } else {
>> +        _FDT((fdt_property(fdt, "ibm,hypertas-functions", hypertas_prop,
>> +                           sizeof(hypertas_prop))));
>> +    }

This prevents migration from newer kernel to older kernel.  Can you
ensure that the fallback to the QEMU implementation works, even though
it is not used in practice?

Paolo